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<TITLE>Re: Information for setting up SMT related parameters on linux 2.6.16 on POWER5</TITLE>
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<DIV dir=ltr><FONT face=Arial color=#000000 size=2>Thanks guys </FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>That answered so many of my questions.
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<DIV dir=ltr><FONT face=Arial size=2>If I were to use these macros from user
space, would they remain set until next reboot or change ? POWER5 allows
priorities 2 through 4 for user apps, so considering this, and the fact that the
normal prioirity is level 4, if a user app resets it to say 2 and then finishes
without changing it back to 4 , would all the subsequent user apps run at the
new level 2. I wonder what I am saying even makes sense, because the kernel
internally throttles the priority for various sections of the kernel code and it
may even overwrite it. </FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>On a slightly unrelated note, I appended
some boot parameters like smt-enabled=on/off to /etc/lilo.conf and unfortunately
I am not able to see any effect and it boots the same way. I am switching from
the AIX world so I maybe doing something dumb, please point out if I am !
This kind of seems to effect the bind processor calls using sys_setaffinity when
there are 4 logical processors 0-3 on two physical processors, bind only allows
me to set affinity to either cpu 0 or 2, this seems weird to me because my
system is booting with two logical cpus and then I set online bit to 1 to turn
the remaining on, thereafter I try binding and havent been very successful.
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<DIV dir=ltr><FONT face=Arial size=2>Thanks for all your replies. </FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV>
<DIV dir=ltr><FONT face=Arial color=#000000 size=2></FONT> </DIV></DIV>
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<DIV> </DIV>
<DIV><BR>Mitesh R. Meswani <BR>Ph.D. Candidate </DIV>
<DIV>Research Associate, PLS2 Group</DIV>
<DIV>Room 106 F, Department of Computer Science</DIV>
<DIV>The University of Texas at El Paso, </DIV>
<DIV>El Paso, Texas 79968<BR>Tel: 915 747 8012 (O)</DIV>
<DIV>Email: mmeswani@utep.edu</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> Segher Boessenkool
[mailto:segher@kernel.crashing.org]<BR><B>Sent:</B> Mon 5/8/2006 5:04
PM<BR><B>To:</B> will_schmidt@vnet.ibm.com<BR><B>Cc:</B> Meswani, Mitesh;
linuxppc-dev@ozlabs.org; Arnd Bergmann; linux-kernel@vger.kernel.org;
cbe-oss-dev@ozlabs.org<BR><B>Subject:</B> Re: Information for setting up SMT
related parameters on linux 2.6.16 on POWER5<BR></FONT><BR></DIV>
<DIV>
<P><FONT size=2>> the HMT_* macros are telling firmware that "this processor
thread <BR>> should<BR>> run at this priority". Typically used
when we're waiting on a <BR>> spinlock.<BR>> I.e. When we are waiting
on a spinlock, we hit the HMT_low macro to <BR>> drop<BR>> our
threads priority, allowing the other thread to use those extra<BR>> cycles
finish it's stuff quicker, and maybe even release the lock <BR>>
we're<BR>> waiting for.
HMT_* is all within the kernel though, no <BR>> exposure<BR>> to
userspace apps.<BR><BR>Actually, those macros translate straight into a single
machine insn.<BR>No firmware is involved. See
include/asm-powerpc/processor.h. For<BR>example:<BR><BR>#define
HMT_very_low() asm volatile("or 31,31,31 # very
low <BR>priority")<BR><BR>You can use those same macros from user space,
although it is CPU<BR>implementation dependent which priorities you can actually
set (you<BR>probably can do low and medium
priority).<BR><BR><BR>Segher<BR><BR></FONT></P></DIV>
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